Equalization processing of an audio signal is commonly used to alter the frequency response of an audio signal to be within a user specified range and is typically achieved by using an equalization filter whose frequency response can be adjusted by a user for one or more reasons, such as the resulting audio signal having improved fidelity, emphasizes certain frequencies or ranges of frequencies, has undesired frequency components such as noise removed, and/or matches perceived timbre of multiple audio signal pieces, such as songs on a CD or multiple compressed MP3 audio signal files. Audio signal equalization is also commonly used in film and television production to improve the quality of the sound, modify and/or match the timbre of audio signal in different scenes or to match individual audio signal streams which comprise a film or television soundtrack. Audio signal equalization can also be used to modify specific frequencies and to make an audio signal perceptually louder, as well as to compensate for frequency dependent deficiencies in an audio signal reproduction apparatus.
Many types of equalizations are known. Such equalizations, however, do not take into account the time varying nature of the audio signal itself.
Recently, perceptual domain processing has been invented that takes into account the variation in the perception of audio depending on the reproduction level of the audio signal. See, for example, International Application PCT/US2004/016964, published as WO 2004111994. Such processing includes determining and adjusting the perceived loudness of an audio signal in an improved manner. A psychoacoustic model is used to calculate a measure of the loudness of an audio signal in perceptual units. Such perceptual domain loudness measure is referred to as specific loudness, and is a measure of perceptual loudness as a function of frequency and time. When applied to equalization, the process is called dynamic equalization (DEQ). What is called “perceptual domain dynamic equalization” (PDEQ) is carried out in a perceptual domain to transform the time-varying perceived spectrum of the audio signal to be closer to a desired time-invariant perceived spectrum. This form of equalization matches a desired target perceived spectrum while preserving the perceived dynamic range. This takes into account the dynamic range and perceived loudness of the audio signal.
Approximate perceptual level dynamic equalization includes making certain approximations in the determining of the perceived loudness to obtain an approximate measure of perceptual loudness as a function of frequency and time. Approximate dynamic equalization using the approximate spectral measure of perceived loudness includes determining a set of frequency and time domain gains to apply in order to transform the time-varying spectral measure of the audio signal to be closer to a desired time-invariant perceived spectrum.
It is known how to achieve such perceptual and approximate perceptual domain dynamic equalization processing. Related invention of U.S. 61/181,206 describes mechanisms for controlling one or more properties of the equalization using one or more pre-determined preset target dynamic equalization spectra, how much equalization to achieve. In the case of more than one preset target perceived spectra, controlling how much the ultimate target perceived spectrum includes each of the preset spectra. Related Application U.S. 61/181,206 also describes user interfaces for a user to store dynamic equalization setting, e.g., as a result of listening to audio and selecting the dynamic equalization setting used for such audio.
It would be advantageous for users to be able to create dynamic equalization settings as dynamic equalization profiles that are usable by others. It also would be advantageous to save such dynamic equalization settings in a predefined format that would be agreed upon by others, so would be accepted by audio playback devices. It also would be advantageous to save such dynamic equalization settings in a predefined format that allows authentication. This would allow users to share their favorite dynamic equalization settings with friends and others, similarly to how people share song playlists on services like iTunes. This also would allow commercial interests to distribute dynamic equalization settings for others to use.
It would be advantageous to use dynamic equalization profiles to process audio to take into account the deficiencies of the reproduction capabilities of a particular audio system, e.g., playback device or element thereof, and to process the audio accordingly. This could include a non-dynamic system calibration spectral profile that compensates for a non-flat spectral response of speakers, for example. Another advantageous use of dynamic equalization profiles is to limit reproduction of some frequencies, for example bass frequencies, which smaller systems may not be able to reproduce at louder levels without introducing distortion.